DE102007011041A1 - Plastic molded tube - Google Patents

Abstract

The invention relates to a plastic molded tube (40), in particular for fuel-carrying return lines in injection systems for internal combustion engines. It comprises an inner tube (42) and an outer coating (12, 44) made of plastic material with connections (18, 20, 46, 48) for further components of the injection system for fuel. The inner tube is designed as a plastic inner tube (42) with at least one pre-bend (54).

Description

State of the art

At Fuel injection systems, such. As pump-nozzle systems (UI) or else High-pressure accumulator injection systems (common rail), come next to one High pressure pump, a high pressure storage body, z. B. pump-nozzle units, and the fuel injectors in the return area for the fuel, d. H. on the low-pressure side of the injection system, plastic pipes for use. About these arranged in the low pressure region of the fuel injection system Plastic molding tubes, the fuel, such. B. taxed amount, the at the operation fuel injectors accumulate, returned to the tank within the fuel system.

The pipes used within the low pressure range are generally made of plastic preformed tubes, due to the installation conditions often have a deviating from the straight shape and arcuately curved. Molded plastic pipes can a shape deviating from the straight line in relation to the inner contour and one of them independent, have geometrically different outer contour. Molded plastic pipes, lead the fuel, have to high strength requirements and beyond have a high security against bursting in the event of an accident. The plastic molding tubes used in the fuel system in the low-pressure side return area can be made with and without throttle, which varies depending on the low pressure range to be held pressure. Plastic tubes forming a bow or a cranked one Section or the like, with respect to the inner contour not or only relatively expensive be formed. Although lets a bow-shaped curved Form inner contour, but no corner radius can be displayed; of Furthermore, a burr freedom is not guaranteed. At fuel-carrying Plastic molded tubes that are in the crash area and usually made of high-strength plastic, there remains a risk of breakage, which increases with decreasing temperatures, resulting in low Outdoor temperature range there is a risk that such a plastic molded tube in the case of Accident bursts and fuel leaks into the environment.

at previously used in series production on fuel injection systems Downcomers For this reason, an overmolded with a plastic jacket Stainless steel tube used. This is done with very elaborate molding process produced. There are very high tolerance requirements to meet the connection geometries to the injection mold, to which at least one to be connected Fuel injector and the manufacturer's side specified Connection scheme to meet. In a variant of the plastic tube in the low pressure region of Fuel injection system, within which a residual pressure level is maintained within the stainless steel tube used one Fixing bushing thrush, which generally achieves this is that the stainless steel is rolled and the throttle preferred is formed as a Buchsendrossel, axially spaced from each other by the two, axially fixed by the rolling process produced recesses in the tube becomes.

The known from the prior art and used in mass production embodiment the plastic tube with integrated stainless steel tube has the reasons above a number of disadvantages, such. B. heavy weight, elaborate shaping processes, Special work to the Fixation of any chokes and the like, so here remedy is to create.

Disclosure of the invention

According to the invention, it is proposed one made of a cold-elastic Plastic injection-molded inner tube in the frame of a plastic molded tube to use, which are formed in largely arbitrary shape can and in particular be made of a different plastic can be considered the one from which the encapsulation of the plastic molding tube is made. With this solution Is it possible, despite high strength and dimensional stability requirements especially when using the inventively proposed plastic molding tubes these in the low pressure range as fuel-carrying pipe parts in fuel systems use.

The Plastic pipe can be cut to length from a continuous casting tube and using a bent thermoplastic molding process. Plastic pipes can be made endless with a strand injection molding process. The plastic pipes are wound on a roll and can open any length be separated. This manufacturing process is particularly inexpensive and of consistently good quality. The inside diameter comes a special meaning, because of this by the Spritzwergzeugkern of the injection mold is sealed against the injection pressure. In contrast, at Use of stainless steel pipes both the connection geometry as well formed the sealing geometry to the tool in high accuracy become. The resulting tolerances with respect to the Bending radius' can be clear to be taller, because only the inner diameter of a connection dimension to the injection mold represents.

Is in the example of a strand Gießrohr cut plastic pipe provided with a throttle, the throttle formed for example as a bushing throttle can already be embedded during the bending process thermoplastic in the material of the plastic pipe. Alternatively, it is quite possible to additionally provide the bushing throttle with a groove extending in the circumferential direction, so that higher forces can be absorbed by it without this moving in the axial direction relative to the jacket of the inner pipe.

at another conceivable embodiment of the invention proposed Plastic molding tube can with lower tolerance requirements the throttle this also formed directly in the material of the inner tube which allows a further cost reduction, since a separate female type trained throttle component can then be omitted. The inventively proposed Plastic molded tube has in terms of its external geometry in series production used geometry, so that no modifications regarding of the installation are required. The contour of the inner tube of the plastic molded tube is chosen that this is within the required external encapsulation. The length is preferred of the inner tube made of plastic chosen so that a sufficient wall thickness of the inner tube enveloping Material material of the encapsulation can be ensured. The material, out the enveloping one Encapsulation is made, is not necessarily the one from which the inner tube is injection molded or continuously cast. The at the previously known solution formed on stainless steel tube sealing geometries are proposed according to the invention solution following now formed in the plastic extrusion of the inner tube. The preferred with a smooth surface Trained plastic inner tube is preferably thermoplastic bent so that the contour for insertion into the injection mold, d. H. its cavity for the production of the enveloping Plastic injection is dimensionally stable. To ensure crash safety, the plastic inner tube is preferably made of cold-elastic plastic, resulting in the break of the plastic inner tube enveloping Encasing the inner tube prevents leakage of the fuel. For support the inner tube within the injection mold during the Overmolding and the concomitant production of the inner tube enveloping Encapsulation is preferred supporting cores used in the plastic tool, which in the course of the injection process be wholly or partially pulled out to the support points to be able to form a closed plastic layer. In order to is achieved that at replacement the inner tube of this enveloping encapsulation no leaks arise. The inner contour of the plastic inner tube and the contour the plastic inner tube enveloping encapsulation are coordinated in such a way that a continuous core both the inner geometry forms as well as a support of the Plastic inner tube against the occurring during the injection process Apply injection pressure can.

Becomes a plastic inner tube required to integrate into a throttle is, the throttle as a separate component, preferably in the arc be fixed to the plastic inner tube. In an advantageous way the throttle is installed before bending the plastic inner tube, so that the throttle already thermoplastic in the form of a Ringverstemmung can be embedded in the plastic tube. The throttle can be preformed thermoplastic in the plastic inner tube and during the injection process by a paragraph of a mandrel, with a low Dive into the throttle to ensure dimensional accuracy while the injection process are fixed.

One Another advantage of the inventively proposed plastic molding tube is to be seen in that when using an endless tube a largely any course of the inner contour is possible without a built To use insert.

Brief description of the drawings

Based In the drawings, the invention will be described below in more detail.

It shows:

1 the embodiment of the return pipe previously used in series production with a stainless steel pipe enclosed by a plastic jacket with connecting geometries formed thereon,

2 a cut through the in 1 illustrated, used in series return pipe with stainless steel pipe,

3 the inventively proposed plastic molding tube with plastic inner tube and this enveloping encapsulation,

4 a section through the in 3 illustrated embodiment of the inventively proposed plastic molding tube,

5 in the plastic inner tube of the inventively proposed plastic molding tube retracted support cores for fixing in the plastic injection mold and

6 the representation of a in the Kunststof Finnenrohr inserted throttle element in the form of a Buchsendrossel.

embodiments

The representation according to 1 is to take a view of a known from the prior art forming tube.

From the illustration according to 1 shows that the molded tube shown there 10 an encapsulation 12 made of a plastic material, which in turn is a stainless steel tube 14 encloses. At the overmoulding 12 of the form tube 14 is a by reference 16 hinted plateau sprayed. The stainless steel pipe 14 has at one end on the material of the stainless steel tube 14 trained connection flange 18 and at the other end an exposed connector 20 on. Below the connection flange 18 of stainless steel pipe 14 is at this a sealing ring receptacle on which, for example, an elastically deformable O-ring can be added.

The encapsulation 12 of the form tube 10 as shown in 1 further includes a bore 22 with which the composite component molding tube 10 , the stainless steel pipe 14 and the overmoulding 12 comprehensive, is mounted in the engine compartment of a motor vehicle.

2 shows a section through the in 1 illustrated, known from the prior art molding tube.

From the illustration according to 2 it turns out that, as in 1 indicated below the connection flange 18 at the upper end of the stainless steel tube 14 an O-ring recording 36 located. 2 shows that the stainless steel tube 14 a 90 ° bend 24 describes and has two different lengths, straight sections. reference numeral 26 refers to the wall of the stainless steel pipe 14 , which is essentially constant along the entire pipe run. The stainless steel pipe 14 is symmetrical to its tube axis 28 educated. The sectional view according to 2 Furthermore, it can be seen that there is a bushing throttle in the pipe cross-section 30 located. The book thrush 30 is in the illustration according to 2 shown as a separate fitting and includes a throttle cross section 32 , The axial fixation of the bushing restrictor 30 done by two curls 34 that are in the pipe wall 26 of stainless steel pipe 14 are executed to the book throttle 30 in the axial direction in the flow cross-section of the stainless steel tube 14 to fix. Another roll 34 is located below the stainless steel tube 14 trained connection flange 18 , This serves for the mechanical clamping of the stainless steel tube 14 and the overmoulding 12 made of plastic.

From the representations according to the 1 and 2 shows that the molded tube shown there 10 a composite component made of a metallic stainless steel tube 14 and a plastic material from which the encapsulation 12 is manufactured, represents. For connecting the stainless steel pipe 14 , which on the one hand has a certain weight, are both the connecting flange 18 , the connector 20 , the 90 ° bend 24 as well as the respective rollings 34 for fixing the bushing thrush 30 in the context of pre-machining operations required before the plastic extrusion can be applied. That in the 1 and 2 illustrated, known from the prior art molding tube 10 has a relatively high weight and is overall relatively expensive to produce.

3 shows an embodiment of the inventively proposed plastic molding tube in perspective view.

From the illustration according to 3 shows that the inventively proposed plastic molding tube 40 a 90 ° bend 24 having plastic inner tube 42 contains, which in turn from a likewise made of plastic Außenumspritzung 44 is completely enclosed. At the outer extrusion 44 on the one hand is a flange connection 46 molded on the other hand, a fitting in a tubular form, see reference numerals 48 , educated. These components, ie the connection points 46 . 48 , are at the in 1 and 2 illustrated embodiment of a forming tube 10 with a stainless steel tube 14 on the stainless steel pipe 14 to train separately in separate operations. In the production of external extrusion 44 the inventively proposed plastic molding tube 40 Within a plastic injection molding machine or a plastic injection molding tool, the connection flange 46 and the tubular connector 48 immediately during the production of the outer extrusion 44 at the outer extrusion 44 getting produced. This goes from the representation according to 3 out. Furthermore, the O-ring holder 36 also during the production of the molded flange 46 at the outer extrusion 44 be produced by plastic injection molding, without separate operations would be required. The lateral surface of the external extrusion 44 enclosed plastic inner tube 42 is by reference numerals 50 characterized. The plastic inner tube is preferred 42 installed as a preformed, separated from a continuous casting tube, and by way of a thermoplastic process is in the originally straight plastic inner tube 42 after cutting the same 90 ° bend 24 , to give an example, made. Instead of in 3 illustrated 90 ° arc 24 on the plastic inner tube 42 Other degrees of curvature other than 90 ° can also be produced. The same applies to a pre-bend 54 that are not in the drawing plane according to 3 , ie the xy-plane, but, for example, in the xz or another, graphically in 3 not shown level. For the sake of completeness it should be mentioned that that of the external extrusion 44 overmoulded plastic inner tube 42 a cross section 52 which has an in 3 not shown throttle body may contain, if it is necessary to maintain a certain return pressure level in the low pressure range.

From the illustration according to 4 is a cut through the in 3 shown in perspective view, according to the invention proposed plastic molding tube 40 , which is made entirely of plastic material, forth.

4 is also the O-ring receptacle below the molded flange 46 removable. 4 shows that the outer extrusion 44 made of plastic material, the lateral surface 50 of the plastic inner tube 42 contacted and this completely encloses, leaving the plastic inner tube 42 according to its contour completely from the external extrusion 44 is surrounded. The geometry of the outer extrusion 44 Therefore, it depends on the preformed molding of the plastic inner tube 42 which preferably acts as a cut-continuous casting tube section inserted into the plastic injection molding tool and can be fixed in this, for example via support cores, before the outer extrusion 44 made of plastic material. The continuous casting tube, of which individual plastic inner tubes are preferred, is concerned 42 be cut to a, which is made of a cold-elastic plastic material. The production of the plastic inner tube 42 From a cold-elastic plastic raw material offers the advantage that in the event of an accident, the plastic inner tube 42 even if the external extrusion is damaged 44 does not burst open, but remains tight, so that in this fuel-carrying component of a fuel injection system for internal combustion engines in the event of an accident, no fuel leaking into the environment.

The representation according to 4 can be seen that the 90 ° arc 24 the pre-bend 54 represents. This pre-bend is preferred 54 , which in this embodiment as 90 ° arc 24 is formed, by way of a thermoplastic process after cutting the plastic inner tube 42 produced by the continuous casting tube. During the ther moplastic process for generating the pre-bend 54 of the plastic inner tube 42 a throttle point can optionally in the flow cross-section 52 of the plastic inner tube 42 getting produced. In the event that only small tolerance requirements are to be met, the throttle point, for example, by a deformation in the pipe wall of the plastic inner tube 42 , ie by a deformation of the made of cold-elastic material Stranggießrohres, can be achieved, so that by the opposite from each other at a smaller distance walls of the plastic inner tube 42 a throttle cross-section is formed.

On the other hand, a separate component designed, for example, as a bushing throttle can also be produced by means of the thermoplastic process before the at least one pre-bend is produced 54 in the flow cross-section 52 of the plastic inner tube 42 be inserted from cold elastic plastic and by generating, for example, a 90 ° bend 24 during the thermoplastic process in the plastic inner tube 42 within the 90 ° arc 24 be embedded.

The representation according to 5 is a plastic inner tube of the invention proposed form tube to remove, which is fixed by support cores of the injection molding tool.

As 5 is removable, includes the forming tube 40 , as proposed according to the invention, in addition to the prefabricated, preferably designed as a cut continuous casting tube plastic inner tube 42 with previously made, at least one pre-bend 54 the outer extrusion 44 , This in turn has a molded connection flange by way of the plastic injection molding process 46 and a tubular connector formed 48 on. Below the molded connection flange 46 is the already mentioned O-ring recording 36 , As shown in the illustration 5 shows, includes the plastic inner tube 42 next to here as a 90 ° bend 24 trained at least one pre-bend 54 a first straight section in a length 62 and a second straight section in a further length 64 , 5 shows that in one by the lengths 62 . 64 predetermined insertion depth 60 in the cross section 52 of the plastic inner tube 42 a first support core 56 and a second support core 58 are inserted. To damage the inner wall of the cross section 52 of the plastic inner tube 42 To avoid, have the first and the second support core 56 . 58 each rounded support core ends 66 on. These allow a damage-free and low-friction insertion of the support cores 56 . 58 in the cross section 52 of the plastic inner tube 42 ,

The plastic inner tube 42 manufactured from the cold-elastic plastic material and by means of the thermoplastic process with at least one pre-bend 54 provided by the first support core 56 or the second supporting core 48 during the formation of the outer extrusion 44 fixed and held in plastic injection mold. The lateral surface 50 of the plastic inner tube 42 is preferably formed smooth and may optionally be pretreated with an adhesion primer. To support the introduced as a preform in the injection mold plastic inner tube 42 during the overmolding with the material from which the external extrusion 44 is made, support the two support cores 56 . 58 this off and become in the course of the injection molding process wholly or partly from the cross section 52 pulled out to reach at the support points a closed plastic layer. This ensures that when detaching the plastic inner tube 42 from the outer extrusion 44 no leakage occurs. In addition to the two support cores 56 . 58 , which is the plastic inner tube 42 are supported against the injection pressure during the entire injection molding process and at the same time seal, are to the outer surface of the plastic inner tube 42 provided radially in the injection mold a plurality of fixing punches, which the plastic inner tube 42 fix until the injection mold is closed and the support cores 56 . 58 in the plastic inner tube 42 retracted. The Fixierstempel are preferably partially or completely pull back before the start of Spritzgießnachdrückens, so that a closed plastic surface to the plastic inner tube 42 forms.

The inner contour of the plastic inner tube 42 and the outer extrusion 44 are coordinated so that a continuous core forms both the inner geometry and possibly the support of the plastic inner tube 42 takes over against the pressure prevailing in the plastic injection molding injection pressure.

From the illustration according to 5 also shows that the support core ends 66 of the first support core 56 or the second support core 58 of the plastic injection mold so far in the 90 ° bend 24 as which the pre-bend 54 is executed in this embodiment, are inserted, that the curvatures of the support core ends 66 on the inner wall of the plastic inner tube 42 issue.

The external extrusion 44 is made of a material that has good form and strength properties even at high engine compartment temperatures. The plastic material for the plastic inner tube 42 In contrast, it must have a particularly good notched impact strength at lower temperatures.

From the illustration according to 6 is an embodiment of the inventively proposed plastic molded tube with throttle point.

From the illustration according to 6 can be seen that in this embodiment of the inventively proposed plastic molding tube 40 the plastic inner tube 42 at a position 68 a throttle formed as a bushing throttle comprises. The plastic inner tube 42 is cut to length from a continuous casting tube of cold-elastic plastic material before insertion into the injection mold and by means of a thermoplastic process with at least one pre-bend 54 Mistake. Prior to performing the thermoplastic process to produce the at least one pre-bend 54 in the plastic inner tube 42 can in this for example the book thrush 30 be inserted until this is at the installation position 68 located. Thereafter, the generation of the at least one pre-bend takes place 54 in the xy-plane or in a plane perpendicular to it, for example for the generation of the reference numeral 24 indicated 90 ° arc. Instead of in the 3 to 6 illustrated 90 ° arc 24 If desired, it can be designed in any number of degrees according to the installation conditions or in other orientations with respect to the illustrated plane of drawing.

Is that as a book thrush 30 For example, trained throttle element in the still straight portion of the plastic inner tube 42 inserted, so takes place during thermoplastic deformation of the plastic inner tube 42 the embedding of the book thrush 30 in the soft plastic material of the plastic inner tube 42 and its clawing with the inner wall. To enable the absorption of higher axial forces, the bushing restrictor 30 also grooves or elevations or depressions in the form of grooves, which an undercut with the soft plastic material during the formation of the at least one pre-bend 54 enable. In this case, for example, by the insertion position of the two mandrels 60 respectively 62 the installation position 68 the book thrush 30 determined and during the training of Außenumspritzung 44 to be kept.

In a further possible embodiment of the inventively proposed plastic molding tube 40 can the throttle cross-section 32 optionally also be generated by the fact that the pipe wall 26 of the plastic inner tube 42 is deformed so that the opposing wall sections a throttle cross-section 32 form. This is possible, for example, if lower tolerance requirements for the plastic molding tube 40 - depending on the purpose - can be made. This is possible, for example, if low tolerance requirements are placed on the throttle cross-section, since the manufacturing accuracy of plastic is generally lower than at Metallic materials that are more sensitive to temperature and pressure changes due to the high coefficients of thermal expansion and smaller moduli of elasticity.

6 can also be seen that in this embodiment, the first support core 56 or the second support core 58 , each with rounded support core ends 66 , until the 90 ° bend 24 protrude. The insertion depths 60 of the first support core 56 or the second support core 58 depend on the length 62 the first straight section or the length 64 the second straight section of the preformed plastic inner tube 44 , Also in this embodiment are the rounded support core ends 66 preferably on the inner wall of the flow cross-section 52 of the fuel-carrying plastic inner tube 42 at. As already mentioned, the at least one pre-bend 54 in the plastic inner tube 42 also have other curvatures than 90 ° and in one in the 3 to 6 not shown, which is perpendicular to the plane of the drawing shown, be formed.

Claims (10)

Plastic tube ( 40 ), in particular for fuel-carrying return lines in injection systems for internal combustion engines, an inner tube ( 42 ) and an outer coating ( 12 . 44 ) made of plastic material, with connections ( 18 . 20 . 46 . 48 ) for further components of a fuel injection system, characterized in that the inner tube as a plastic inner tube ( 42 ) with at least one pre-bend ( 54 ) is executed. Plastic molded tube according to claim 1, characterized in that the plastic inner tube ( 42 ) is made of a cold-elastic plastic. Plastic molded tube according to claim 1, characterized in that the plastic inner tube ( 42 ) is a cut continuous casting tube and the at least one pre-bend ( 54 ) is produced by a thermoplastic process. Plastic mold tube according to claim 1, characterized in that in the at least one pre-bend ( 54 ), in particular as a 90 ° bend ( 24 ), a throttle ( 30 ) is trained. Plastic molded tube according to claims 3 and 4, characterized in that the throttle ( 30 ) is designed as a Buchsendrossel which in the thermoplastic process in the cross section ( 52 ) of the plastic inner tube ( 42 ) is embedded. Plastic molded tube according to claim 1, characterized in that the outer extrusion ( 44 ) a molded flange ( 46 ), a molded, freely accessible tubular connecting piece ( 48 ) and at least one recess ( 36 ) for receiving a sealing element. Plastic molded tube according to claim 1, characterized in that in the plastic inner tube ( 42 ) by deformation of the pipe wall ( 26 ) a throttle cross-section ( 32 ) is formed. Method for producing a plastic molded tube ( 40 ) according to claim 1 with the following method steps: a) the cutting to length of the plastic inner tube ( 42 ) of a continuous casting material produced from cold-elastic plastic material, b) producing at least one pre-bend ( 54 ) in the cut plastic inner tube ( 42 ), c) the encapsulation of the plastic inner tube ( 42 ) with an outer coating ( 44 ) under formation of connection geometries ( 46 . 48 ) at the outer extrusion ( 44 ), d) supporting the plastic inner tube ( 42 ) during process step c) in the cross section ( 52 ) of the plastic inner tube ( 42 ) retracted support cores ( 56 . 58 ), e) the temporary fixing of the plastic inner tube ( 42 ) during the process step c) by the on the outer surfaces of the plastic inner tube ( 50 ), and f) the fixing punches according to method step e) are withdrawn in order to obtain a closed plastic surface against the process end of method step c). A method according to claim 8, characterized in that method step b) is carried out by a thermoplastic process and a throttle, preferably a Buchsendrossel ( 30 ), before the generation of the at least one pre-bend ( 54 ) in the cross section ( 52 ) of the plastic inner tube ( 42 ) and in the production of the at least one pre-bend ( 54 ) in the plastic inner tube ( 42 ) is embedded. A method according to claim 8, characterized in that the generation of a throttle cross-section ( 32 ) in the plastic inner tube ( 42 ) by a deformation of the pipe wall ( 26 ) takes place in the context of a thermoplastic process.